Ecosystems, 2018, Vol.21(2), pp.280-296
To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1007/s10021-017-0148-6 Byline: Ina Christin Meier (1), Florian Knutzen (1), Lucia Muriel Eder (1,2,4), Hilmar Muller-Haubold (1), Marc-Oliver Goebel (3), Jorg Bachmann (3), Dietrich Hertel (1), Christoph Leuschner (1) Keywords: coarse roots; European beech; fine roots; mature trees; optimal partitioning theory; precipitation gradient; rooting depth; root morphology; root-to-shoot ratio Abstract: Abstract When applied to climate change-related precipitation decline, the optimal partitioning theory (OPT) predicts that plants will allocate a larger portion of carbon to root growth to enhance the capacity to access and acquire water. However, tests of OPT applied to the root system of mature trees or stands exposed to long-term drying show mixed, partly contradicting, results, indicating an overly simplistic understanding of how moisture affects plant-internal carbon allocation. We investigated the response of the root system (0--240 cm depth) of European beech to long-term decrease in water supply in six mature forests located across a precipitation gradient (855--576 mm mean annual precipitation, MAP). With reference to OPT, we hypothesized that declining precipitation across this gradient would: (H1) cause the profile total of fine root biomass (FRB roots 〈2 mm) to increase relative to total leaf mass (H2) trigger a shift to a shallower root system and (H3) induce different responses in the depth distributions of different root diameter classes. In contradiction to H1, neither total FRB (0--240 cm) nor the FRB:leaf mass ratio changed significantly with the MAP decrease. The support for H2 was only weak: the 95% rooting depth of fine roots decreased with decreasing MAP, whereas the maximum extension of small coarse roots (2--5 mm) increased, indicating contrasting responses of different root diameter classes. We conclude that long-term decline in water supply leads to only minor adaptive modification with respect to the size and structure of the beech root system, with notable change in the depth extension of some root diameter classes but limited capacity to alter the fine root:leaf mass ratio. It appears that OPT cannot adequately predict C allocation shifts in mature trees when exposed to long-term drying. Graphical Abstract Author Affiliation: (1) 0000 0001 2364 4210, grid.7450.6, Plant Ecology, Albrecht von Haller Institute for Plant Sciences, University of Goettingen, 37073, Goettingen, Germany (2) 0000 0004 1936 9756, grid.10253.35, Soil and Hydraulic Geography, Faculty of Geography, University of Marburg, 35032, Marburg/Lahn, Germany (3) 0000 0001 2163 2777, grid.9122.8, Institute for Soil Science, University of Hannover, 30419, Hannover, Germany (4) 0000 0004 0491 7318, grid.419500.9, Max Planck Institute for Biogeochemistry, 07745, Jena, Germany Article History: Registration Date: 08/04/2017 Received Date: 23/02/2016 Accepted Date: 28/03/2017 Online Date: 08/05/2017 Article note: Author Contributions CL, ICM, and DH conceived of or designed the research project. FK, MOG, LME, and HMH performed research. ICM analyzed the data. ICM, CL, MOG, and JB wrote the manuscript. Electronic supplementary material The online version of this article (doi:10.1007/s10021-017-0148-6) contains supplementary material, which is available to authorized users.
coarse roots ; European beech ; fine roots ; mature trees ; optimal partitioning theory ; precipitation gradient ; rooting depth ; root morphology ; root-to-shoot ratio
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